FIG. 1 is a diagram of an interlaced video frame 10, which includes an even video field 12 and an odd video field 14. The even field 12 includes the even lines a0, a2, a4 . . . a(n-1) of the frame 10, and the odd field 14 includes the odd lines b1, b3, b5 . . . bn of the frame 10. A video source (not shown) such as a video camera generates the even field 12 at a time t0 and generates the odd field 14 at a subsequent time t1, and a video display (not shown in FIG. 1) displays the fields 12 and 14 in the same sequence. For example, according to the National Television Standards Committee (NTSC) video standard, which has been in existence for over 50 years, a video source generates and a video display displays one field 12 or 14 every {fraction (1/60)}th of a second, and thus respectively generates and displays one frame 10 every {fraction (1/30)}th of a second. But even though the display displays the fields 12 and 14 at different times, the relatively slow frequency responses of the display and the human eye cause a viewer to perceive that the display is displaying the fields 12 and 14 simultaneously. Thus, the viewer perceives the frame 10 as a single image instead of two sequential partial images.
Many modern video applications, however, generate streams of non-interlaced, i.e., progressive, video frames. For example, most applications of the new High-Definition Television (HDTV) standards such as MPEG (Motion Pictures Experts Group) call for the generation and display of an entire frame 10 approximately every {fraction (1/60)}th of a second. Because such MPEG video sources and displays respectively generate and display all the lines of a progressive frame at one time and not at two sequential times, progressive frames contain little if any motion blurring.
Because many existing video sources generate interlaced video, and because many existing video works are recorded in an interlaced format, one may wish to convert a stream of interlaced video frames into a stream of progressive video frames that are compatible with HDTV systems. For example, one may wish to convert a VHS signal from a VCR (not shown) into a progressive video signal for display on an HDTV display (not shown in FIG. 1).
Still referring to FIG. 1, a simple technique for de-interlacing the interlaced frame 10 is to merge the fields 12 and 14 into a resulting progressive frame that is displayed twice in a row at the frame-display rate. For example, in the MPEG standard described above, a display displays this resulting progressive frame and then displays it again {fraction (1/60)}th of a second later. But because the fields 12 and 14 were generated at different times t0 and t1, the resulting progressive frame may contain blurred regions, particularly if there were changes in the image contents, i.e., motion, between the times t0 and t1. Thus unfortunately, this technique often results in a video stream of relatively poor visual quality by HDTV standards.
Another technique for de-interlacing the video frame 10 is to generate respective complimentary filler fields for the original fields 12 and 14. That is, for the even field 12, one “fills” the missing odd lines with odd filler lines, and for the odd field 14, one fills the missing even lines with even filler lines.
One approach to this filler technique is to spatially interpolate the filler pixels of the filler lines from the values of neighboring original pixels within the same field. This approach is typically most accurate when there is significant motion between the original fields. Unfortunately, many spatial interpolation approaches have a tendency to falsely interpolate a thin line as a directional edge, and thus introduce artifacts into the resulting progressive frame.
An alternative approach is to temporally interpolate the values of the filler pixels from the values of corresponding original pixels in adjacent complimentary original fields. This approach is typically most accurate when there is little or no motion between the original fields.
Because many interlaced video streams have some segments that exhibit significant inter-field motion and other segments that exhibit little or no inter-field motion, another approach, often called a hybrid approach, combines the spatial and temporal interpolation approaches. For example, one hybrid approach varies the relative weightings of the temporal and spatial interpolation approaches based on the magnitude of inter-field motion. The greater the magnitude of inter-field motion, the more heavily weighted the spatial interpolation approach; conversely, the lower the magnitude of inter-field motion, the more heavily weighted the temporal interpolation approach.
Unfortunately, many hybrid techniques sometimes fail to detect significant inter-field motion, and thus assign improper weightings to the spatial and temporal approaches. Although some of these techniques can be modified to overcome this defect, such modifications often require an impractical amount of memory.